The invention is related to an actuator, comprising a housing which contains a screw mechanism and a motor which is drivably connected to the screw mechanism, said screw mechanism providing a linear movement in response to a rotational movement of the motor, and comprising a screw and a nut one of which is supported rotatably with respect to the housing by means of a bearing.
Such actuator is known from WO-A-9603301.
Having regard to the fields of application of these actuators, it is generally desired to obtain limited overall dimensions and low weight in combination with a low cost price. For instance, actuators of this kind are applicable in disc brakes for the automative industry. A relatively low weight of the actuator is of importance with respect to minimizing the unsprung weight of a vehicle.
The object of the invention is to provide an actuator which is improved with respect to the criteria before. This object is obtained in that support means are provided which extend axially with respect to the screw mechanism, said support means engaging the housing, and supporting at least one of the screw mechanism and the motor.
The support means enable a stable positioning or centring the actuator, and provide an accurate and repeatable displacement in response to control signals. Moreover, the support means may partly or completely be accommodated within the screw mechanism, whereby the overall dimensions are reduced.
The support means as contained in the actuators according to the invention may be connected to the housing in several ways. According to a first embodiment, the support means may comprise a shaft or tube member which is stationary fixed to the housing, the rotor and one of the nut or screw being rotationally supported with respect to the shaft or tube member.
Said shaft or tube member at one end extends into the screw mechanism, and carries a support bearing at or near said end for supporting axial loads exerted on the screw mechanism.
For an improved load support function, the support bearing may be carried out as a four-point contact bearing, the loading angle of the pair of contact points which take up the axial compressive force on the screw mechanism being smaller than the other loading angle. Furthermore, the support bearing is preferably a full complement bearing.
According to a particularly preferred embodiment, the support bearing is situated within the screw mechanism. Said support bearing rotatably supports the screw of the screw mechanism.
Furthermore, the screw may be ring-shaped or sleeve-shaped, and the outer race of the support bearing may be partly of fully integrated in the inner surface of said ring-shaped or sleeve-shaped screw.
Moreover, the inner race of the support bearing may be partly or fully integrated in the shaft or tube member.
For purposes of controlling the actuator load and thus the brake force, the shaft or tube member engages the housing through a load cell. Said load cell may comprise a piezo-electric material, or a strain-gauge embedded in a foil.
According to a second, alternative embodiment the support means comprise a shaft or tube member which is rotatably connected to the housing. Said shaft or tube member is arranged for transferring a rotational movement between motor and screw mechanism. In a simple embodiment, the rotor is connected to the shaft or tube member.
The shaft or tube member is supported with respect to the housing by means of a support bearing for transferring axial forces exerted on the screw mechanism. In this case as well, the support bearing engages the housing through a load cell.
The screw may be fixed to the shaft or tube member; alternatively, the nut is fixed to the shaft or tube member.
In a preferred embodiment, the screw is axially displaceable and non-rotatable with respect to the housing, and the nut is rotatably supported with respect to the housing by means of a support bearing. Said support bearing may engage the housing through a load cell.
The motor may engage the screw mechanism through a reduction gear mechanism. Said reduction gear can be contained in a reduction gear module.
The invention is also related to a brake calliper for a disc brake, comprising a claw piece carrying two opposite brake pads between which a brake disc can be accommodated, and an actuator for displacing the brake pads towards and from each other, said actuator comprising a housing connected to the claw piece and containing a screw mechanism and a motor which is drivably connected to the screw mechanism, said screw mechanism providing a linear movement in response to a rotational movement of the motor, and comprising a screw and a nut one of which is supported rotatably with respect to the housing by means of a bearing. According to the invention, said actuator is provided with support means which extend axially with respect to the screw mechanism, said support means engaging the housing, and supporting the screw mechanism.
Several further embodiments are conceivable as well. For instance, all or some of the components of the actuator may be obtained by means of a hard turning operation, or may be coated with a diamond-like carbon coating. In this way, wear may be reduced. Also, the actuator may be lubricated and sealed for life.
The gears applied in the gear reduction may consist of a, metallic, a non-metallic or a powder material.
The drive means can be electrical, hydraulic, pneumatic or mechanically induced by e.g. a spring.
The support shaft or tube may comprise an external flange which forms a unity therewith, or which is (laser)welded, bolted, glued, soldered etcetera thereto.
The recirculating means for the balls or rollers of the ball screw mechanism (grooves, holes or tubes) may be located in the nut or the screw.